let intervalID;
function startChange() {
    if (!intervalID) {
        intervalID = setInterval(changeRandomColor, 1000);
    }
}
function changeRandomColor() {
    const randomColor = Math.floor(Math.random() * 16777215).
   toString(16);
    document.body.style.backgroundColor = `#${randomColor}`;
   }
document.getElementById("start").addEventListener("click", startChange);
/*let intervalID = setInterval(myCallback, 1000);
function myCallback() {
 console.log(Date.now());
}
function stopChange() {
 clearInterval(intervalID);
}
document.getElementById("stop").addEventListener("click", stopChange);
let intervalID = setInterval(myCallback, 1000, "你好");
function myCallback(a) {
 console.log(a, Date.now());
}
let intervalID;
function startChange() {
 if (!intervalID) {
 intervalID = setInterval(changeColor, 1000);
 }
}
function changeColor() {
 if (document.body.style.backgroundColor !== "black") {
 document.body.style.backgroundColor = "black";
 document.body.style.color = "white";
 } else {
 document.body.style.backgroundColor = "white";
 document.body.style.color = "black";
 }
}
document.getElementById("start").addEventListener("click", startChange);
function changeRandomColor() {
 const randomColor = Math.floor(Math.random() * 16777215).
toString(16);
 document.body.style.backgroundColor = `#${randomColor}`;
}
intervalID = setInterval(changeRandomColor, 1000);
*/
